<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>

        .box {
            overflow: hidden;
            width: 400px;
            height: 400px;
            background-color: red;
        }

        .son {
            margin-top: 50px;
            width: 200px;
            height: 200px;
            background-color: skyblue;
        }


    </style>
</head>
<body>

    <div class="box">
        <div class="son"></div>
    </div>
    
</body>
</html>